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University of California Publications in Zoology [Vol. 27 
To summarize the results of the experiments: We have, in these three species, 
a graduated series so far as the relation of the power of autotomy and the presence 
of these poison glands are concerned. Batrachoseps yields comparatively little 
poisonous secretion when stimulated; Plethodon yields it abundantly on the tail 
and Diemyctylus pours it out very generally over the dorsal surface of the body. 
Batrachoseps is eaten with avidity by snakes. Plethodon is not rejected, but 
Diemyctylus seems not to be taken at all as food. In Batrachoseps, where the 
secretion is slight, autotomy occurs on little provocation and at almost any point. 
In Plethodon, where the secretion is restricted to the tail though abundant there, 
autotomy occurs only as a last desperate resource and but in one region. In 
Diemyctylus where the secretion is copious and general over the body autotomy 
does not take place. 
Finally, passing from the region of fact and entering that of hypothesis, it 
seems fair to conclude that we have in these three species a case of adaptive corre- 
lation between autotomy and protective secretion. Batrachoseps appears to have, 
in its great tail-shedding power, some compensation for its limited defensive 
glands. Diemyctylus has no need of this, being sufficiently safe, so far as one 
means of defense is concerned, in its oAvn abundant secretion. And, finally, it 
seems probable that when its tail secretion fails the Plethodon, this species sheds 
that organ to supplement the inadequacy of poison. 
Hydromantes platycephala (Camp). Mount Lyell Salamander 
Spelerpes platycephalus Camp (1916b, pp. 11-14, figs. 1-5). Original de- 
scription, type from head of Lyell Canon, 10,800 feet, Yosemite National 
Park, California. 
Spelerpes platycephalus, Grinnell and Camp (1917, p. 132, fig. 2). Range. 
Eurycea platycephala, Stejneger and Barbour (1917, p. 20). Range. 
Lyell Salamander, Grinnell and Storer (1921, p. 178). Occurrence. 
Hydromantes platycephalus, Dunn (1923a, p. 40). Relationships. 
Hydromantes platycephala, Stejneger and Barbour (1923, p. 17). Range. 
Eurycea platycephala, Grinnell and Storer (1924, p. 652, pi. 60/). General 
account of discovery. 
Diagnosis . — Size moderate among California salamanders, total 
length up to 99.4 millimeters (4 inches) ; naso-labial groove present; 
head depressed, breadth about three times greatest thickness ; inter- 
orbital space greater than length of orbit ; costal folds 12 ; digits half- 
webbed ; parasphenoid tooth patches separated medially ; tongue 
attached only by central pedicel, freely protrusible. 
Comparisons . — Distinguished from other California Caudata except 
Plethodontidae by presence of naso-labial groove and of parasphenoid 
teeth; from Plethodontidae in general by depressed form of head, 
separated patches of parasphenoid teeth, and presence of half-webs 
between the blunt digits. 
Description (based on type and cotype, nos. 5693 §, 5694 J 1 , Mus. 
Vert. Zool.). — General form and especially head, depressed; muzzle 
truncate oval in outline from above, thin and evenly rounded in pro- 
file; lower jaw overhung by muzzle ; no canthus rostralis; external 
nares very small, terminal ; length of muzzle equal to orbit ; orbit 
large; interorbital space flat, its width greater than length of orbit; 
